Leaf-Mimicking Solar Cells Generate 47% More Electricity

That smarty Mother Nature is always teaching us lessons on how to make technology better. Scientists at Princeton University were able to achieve major gains in light absorption and efficiency of solar cells after being inspired by the wrinkles and folds on leaves. The team created a biomimetic solar cell design using a relatively cheap plastic material that is capable of generating 47 percent more electricity than the same type of solar cells with a flat surface.

The team used ultra-violet light to cure a layer of liquid photographic adhesive, alternating the speed of curing to create both shallower wrinkles and deeper folds in the material, just like a leaf. The team reported in the journal Nature Photonics that these curves on the surface made a sort of wave guide that channeled more light into the cell, leading to greater absorption and efficiency.

Jong Bok Kim, a postdoctoral researcher in chemical and biological engineering and the paper's lead author said, "I expected that it would increase the photocurrent because the folded surface is quite similar to the morphology of leaves, a natural system with high light harvesting efficiency. However, when I actually constructed solar cells on top of the folded surface, its effect was better than my expectations."

The researchers found that the greatest gains were at the longest (red) end of the light spectrum. Solar cell efficiency typically tapers off at that end of the spectrum, with virtually no light absorbed as it approaches infrared, but the leaf design was able to absorb 600 percent more light from this end of the spectrum.

Plastic solar cells are tough, flexible, bendable and cheap. They have a wide-range of potential applications, but their biggest downfall is that they're much less efficient than conventional silicon cells. A team at UCLA was recently able to achieve an efficiency of 10.6 percent, which put the cells into the 10 - 15 percent efficiency range considered necessary for commercialization. The Princeton teams expects that their leaf-mimicking design could push that efficiency even further because the method can be applied to almost any plastic material.

The curing process also makes the cells stronger because the wrinkles and folds relieve mechanical stresses from bending. A standard plastic solar panel would see an efficiency dive of 70 percent after bending, but the leaf-like cells saw no diminished effects. This tough flexibility could lead to the cells being incorporated in electricity-generating fabrics or windows and walls.